@Krystina & Nelli ,
Bupre and lantus is constipating. I don't know about the other meds you give. It takes up to 3 days for miralax to work. Lactulose should work in about 4-6 hrs.
Ollie started out when after 5 days of not going but getting pumpkin. I started adding miralax twice a day. She started going a small amount. I doubled doses and still no improvement. She just didn't have the muscles to move it through. It took the cardiologist to suggest cisipride in his report and that's when she agreed to it. She didn't agree to lactulose so I had to get that from Canada cuz I need a script here.
I started with lactulose 12 hrs apart in addition to pumpkin and miralax. She went about 36 hrs later. Once she started eventually it turned to diarrhea by next day. So I cut the miralax out, then next time cut the pumpkin out and constipation was back. So by evening dose lactulose out and added miralax back in and needed to tweak though doses until we got it right. Then she started having problems again. Vet said add bulk so psyllium power tried and got her moving again. Now it's back to miralax, lactulose and her subq fluids twice a week (though lately I can't get them in twice). One thing is if I miss one day of lactulose, she doesn't go that night or next day.
You have to try different things, play with the order and doses until you get it right. Make sure lactulose is separated from miralax. I also make sure lactulose is separated from food and meds just in case it could interfere with absorption.